Comfortable and user friendly office equipment which can be readily adapted to a user's individual needs is a prerequisite for creating an office work environment conducive to maximum productivity. Office chairs are an integral part of any office environment and chairs having features which can be adjusted to meet a user's posture requirements clearly play a pivotal role in contributing to a user's comfort level. In particular, chairs having height adjustable backrests or seat backs are important for adapting the chair to the user's posture requirements. The chair seat back is attached to the seat by a support arm which is attached at one end to the seat back while the other end is engaged by a seat back height adjustment mechanism attached to the chair.
Prior art seat back height adjustment mechanisms include a cam rotatably mounted in a bracket. The cam comprises a cylindrical rod having a handle attached thereto. The cam is rotatably mounted between the side walls of the bracket spaced from a back wall of the bracket. The rod is shaped in such a way so that rotation of the rod provides a cam action. The support arm is slidingly received between the bracket back wall and the cam. To lock the seat back at the desired height, the cam is rotated so that the shaped portion of the rod engages the support arm thereby compressing the arm between the cam-shaped portion and the back wall of the bracket.
One drawback to this arrangement is that because the cam is cylindrically shaped and has a smooth outer surface, it is prone to becoming unlocked by slipping to the unlocked position since the cam only exerts pressure on the seat back support arm and does not interlock with it. Secondly, in order for the cam to engage the seat back support arm, the latter must have a specific thickness in order to be effectively engaged by the cam.
Accordingly, it would be advantageous to provide a chair seat back height adjustment mechanism which can be adapted to lock seat back support arms having a range of thicknesses in addition to forming a positive interlocking connection with the support arm.